1. Field of Invention
The present invention relates to laser scanning systems and more particularly, to electronically-controlled damped off-resonant mechanisms for reliably scanning laser beams during bar code symbol reading operations and the like.
2. Brief Description of the Prior Art
Laser scanning bar code symbol scanners are widely used to read bar code symbols on products and packages for identification purposes. Many different techniques exist for scanning laser beams across objects.
One commonly used beam scanning technique involves driving a resonant element bearing a mirror into oscillatory motion within a plane, while a laser beam is directed incident the mirror surface. As the resonant element oscillates, so too does the mirror, causing the incident laser beam to be scanned across a scanning field of substantially planar extent, as well as a bar code symbol disposed therewithin. In general, laser light reflected from the scanned bar code symbol is collected and detected to produce an electrical signal representative of the scanned symbol. Ultimately, the electrical signal is processed in order to decode the scanned symbol and produce symbol character data representative of the decoded symbol.
In U.S. Pat. Nos. 5,168,149, 5,280,165, 5,374,148 and 5,581,067, several different scanning mechanisms are disclosed, in which strips made of Mylar.TM. or Kapton.TM. plastic material are used to realize resonant scanning elements. While such prior art scanning elements are durable, they are not without their shortcomings and drawbacks.
Such prior art laser scanning mechanisms are generally massive and large in comparison to the size of the scanning mirror supported thereby. Prior art laser scanning mechanisms are generally difficult to produce, expensive to manufacture, difficult to precisely tune, and typically require an anti-shock mechanism to protect the scanning element from damage when dropped. Consequently, there are numerous applications where such limitations prevent prior art scanning mechanisms from being used in a commercially feasible manner.
Addressing the shortcomings and drawbacks associated with the above-described scanning mechanism, Applicants hereof have attempted to construct a laser beam scanning mechanism, in which a thin strip of Kapton.TM. film, anchored at its base end and supporting a miniature mirror and a ferrite magnet on its free end, is driven in an off-resonant mode of operation in order to scan a laser beam incident the mirror. While laboring long and hard, Applicants have been unable to consistently manufacture in large volume and at low cost, a laser beam scanning mechanism based on such prior art design principles, without seriously sacrificing the operation and performance thereof.
Consequently, hitherto, Metrologic's ScanQuest.RTM. Laser Scanning Engine (Models 4110 and 4120), in which the above-described scanning mechanism is employed, could not be manufactured in high volume or at low cost.
Therefore, there is a great need in the art for an improved laser scanning mechanism which avoids the shortcomings and drawbacks of prior art laser beam scanning apparatus and methodologies.